🧮 Body Surface Area Calculator (BSA): Mosteller and Du Bois
By Shihab Mia · Reviewed by ToolNimba Editorial Review, health content reviewer · Updated 2026-06-27
This calculator gives an estimate only and is for general information, not medical advice. Body surface area is used in clinical settings such as drug dosing, and the exact value can vary with the formula chosen and with how height and weight are measured. Do not use this result to set or change any medication dose. Always rely on a qualified clinician and the values recorded in your medical records.
Body surface area (BSA) estimates the total external area of your body, expressed in square meters. It is widely used in medicine because many clinical measures, from drug doses to cardiac output, scale better with surface area than with weight alone. Enter your height and weight in metric or imperial units, and this calculator returns your BSA using the Mosteller formula, the version most commonly used in practice because it is simple and accurate.
What is the Body Surface Area Calculator?
Body surface area is the measured or estimated area of the outer surface of the human body. Because it cannot be measured directly without elaborate equipment, it is estimated from height and weight using a formula. The result is reported in square meters, and a typical adult falls somewhere between about 1.5 and 2.0 m2. BSA matters clinically because the size of a person's surface relates more closely than body weight to physiological processes such as metabolic rate, fluid requirements and how the body handles certain drugs.
The Mosteller formula, published in 1987, is the one this tool uses by default. It states that BSA in square meters equals the square root of the product of height in centimeters and weight in kilograms divided by 3600. Its appeal is that it is easy to calculate by hand or on a basic calculator while staying close to older, more complex equations such as the Du Bois and Du Bois formula. For a person who is 170 cm tall and 70 kg, the Mosteller estimate is about 1.82 m2.
Several other formulas exist and remain in clinical use. The classic Du Bois and Du Bois equation from 1916 is BSA equals 0.007184 times height in cm to the power 0.725 times weight in kg to the power 0.425. The Haycock formula is often preferred for infants and small children, while Gehan and George was fitted to a large measured sample, and the Boyd formula was historically used in pediatric oncology. These equations can disagree by a few percent: a BSA of 1.73 m2 by Du Bois may read as much as 0.1 m2 higher under Gehan and George, and the gap widens at the extremes of height and weight.
BSA appears most often in three clinical contexts. In oncology, many chemotherapy doses are written in milligrams per square meter, so the prescriber multiplies that figure by the patient's BSA to get the actual dose. In cardiology, cardiac output is divided by BSA to give the cardiac index in liters per minute per square meter, which lets doctors compare hearts across people of very different sizes. In nephrology, estimated kidney function (eGFR) is normalized to a standard reference BSA of 1.73 m2, and may be de-indexed to a person's actual BSA when body size is unusually large or small.
Average values give useful context for a result. Adult men average roughly 1.9 m2 and adult women roughly 1.6 m2, though both vary widely with build. Children rise steeply with age: a newborn sits near 0.2 to 0.25 m2, a one year old near 0.45 m2, a five year old near 0.75 m2 and a ten year old near 1.1 m2. Because none of these formulas is a direct measurement, the figure should be read as a close estimate rather than an exact number.
For everyday understanding and for most adult calculations the Mosteller result is more than adequate, and it is the value this tool reports. In a hospital, however, the choice of formula, the rounding rules and any dose cap are decided by local protocol rather than personal preference, which is why a general calculator like this one should never be used to set or change a real medication dose.
When to use it
- Understanding a BSA figure mentioned by a doctor or pharmacist, for example in chemotherapy dosing where doses are written in milligrams per square meter.
- Students in nursing, pharmacy or medicine practicing the Mosteller and Du Bois calculations for exams and coursework.
- Estimating body surface area for physiology, sports science or fitness contexts where it is used to normalize measurements.
- Comparing how BSA changes with different heights and weights to build intuition about body size.
- Checking your own figure against the typical adult range of roughly 1.5 to 2.0 m2 out of curiosity.
- Cross checking a value used to index cardiac output or to de-index an eGFR result for an unusual body size.
How to use the Body Surface Area Calculator
- Choose metric (centimeters and kilograms) or imperial (feet, inches and pounds) units.
- Enter your height in the selected units.
- Enter your weight in the selected units.
- Read your body surface area in square meters from the result panel, which updates instantly.
- Compare your figure against the average values in the reference tables below for context.
Formula & method
Worked examples
An adult who is 170 cm tall and weighs 70 kg.
- Multiply height by weight: 170 × 70 = 11,900
- Divide by 3600: 11,900 ÷ 3600 = 3.3056
- Take the square root: sqrt(3.3056) = 1.818
- Round to two decimals: 1.82
Result: BSA ≈ 1.82 m²
A person who is 180 cm tall and weighs 80 kg.
- Multiply height by weight: 180 × 80 = 14,400
- Divide by 3600: 14,400 ÷ 3600 = 4
- Take the square root: sqrt(4) = 2
- Round to two decimals: 2.00
Result: BSA ≈ 2.00 m²
A person who is 5 ft 7 in tall and weighs 154 lb (imperial input).
- Convert height: (5 × 12 + 7) × 2.54 = 67 × 2.54 = 170.18 cm
- Convert weight: 154 × 0.45359237 = 69.85 kg
- Multiply: 170.18 × 69.85 = 11,887.1
- Divide by 3600 and take the square root: sqrt(11,887.1 ÷ 3600) = sqrt(3.3020) = 1.817
Result: BSA ≈ 1.82 m²
Comparing Mosteller with Du Bois for an adult of 180 cm and 85 kg.
- Mosteller: sqrt((180 × 85) ÷ 3600) = sqrt(15,300 ÷ 3600) = sqrt(4.25) = 2.06
- Du Bois: 0.007184 × 180^0.725 × 85^0.425
- 180^0.725 = 44.13 and 85^0.425 = 6.50
- Du Bois: 0.007184 × 44.13 × 6.50 = 2.06
Result: Both formulas give BSA ≈ 2.06 m², showing how closely they agree near average builds.
Mosteller BSA for sample height and weight combinations
| Height (cm) | Weight (kg) | BSA (m²) |
|---|---|---|
| 150 | 50 | 1.44 |
| 160 | 60 | 1.63 |
| 170 | 70 | 1.82 |
| 180 | 80 | 2.00 |
| 190 | 85 | 2.12 |
| 200 | 100 | 2.36 |
Common BSA estimation formulas and their equations
| Formula | Year | Equation (height in cm, weight in kg) |
|---|---|---|
| Mosteller | 1987 | sqrt((height × weight) ÷ 3600). Simplest, used by this tool. |
| Du Bois and Du Bois | 1916 | 0.007184 × height^0.725 × weight^0.425. The classic original. |
| Haycock | 1978 | 0.024265 × height^0.3964 × weight^0.5378. Suited to infants and children. |
| Gehan and George | 1970 | 0.0235 × height^0.42246 × weight^0.51456. Large measured sample. |
| Boyd | 1935 | Logarithmic equation, historically used in pediatric oncology. |
Typical average body surface area by group
| Group | Approximate average BSA (m²) |
|---|---|
| Adult man | 1.9 |
| Adult woman | 1.6 |
| Newborn | 0.2 to 0.25 |
| Child age 1 | 0.45 |
| Child age 5 | 0.75 |
| Child age 10 | 1.1 |
Common mistakes to avoid
- Mixing up the units. The Mosteller formula expects height in centimeters and weight in kilograms. Plugging in inches or pounds without converting gives a wildly wrong answer. Use the imperial toggle so the conversion is handled for you.
- Treating the estimate as an exact measurement. BSA from any formula is a population based estimate, not a direct measurement. Different formulas can differ by a few percent, so do not read more precision into the figure than it carries.
- Using this result for drug dosing. Clinical dosing follows strict protocols about which formula to use, how to round and how to cap the result. Never set or adjust a medication dose from a general calculator. Leave that to a clinician.
- Forgetting children need different handling. Mosteller works for adults and older children, but infants and small children are often estimated with the Haycock formula. The numbers from a generic adult tool may not suit very young patients.
- Assuming every formula gives the same number. Mosteller, Du Bois, Haycock, Gehan and George and Boyd can disagree, sometimes by 0.1 m2 or more at the extremes of size. If a clinician quotes a different value, they may simply be using a different formula.
- Confusing BSA with BMI. Body surface area and body mass index are not the same thing. BMI compares weight to height squared as a measure of weight status, while BSA estimates the physical area of your skin in square meters for clinical scaling.
Glossary
- Body surface area (BSA)
- The total area of the outer surface of the body, estimated from height and weight and reported in square meters.
- Mosteller formula
- A 1987 equation that estimates BSA as the square root of height in cm times weight in kg divided by 3600.
- Square meter (m²)
- The unit BSA is reported in. Most adults fall between roughly 1.5 and 2.0 square meters.
- Du Bois formula
- An older, more complex BSA equation from 1916 that the Mosteller formula closely approximates.
- Haycock formula
- A 1978 BSA equation often preferred for estimating surface area in infants and small children.
- Cardiac index
- Cardiac output divided by BSA, in liters per minute per square meter, used to compare heart performance across body sizes.
- mg/m2 dosing
- A way of prescribing drugs, common in chemotherapy, where the dose is set per square meter of body surface area.
- Indexed eGFR
- Estimated kidney function normalized to a standard reference BSA of 1.73 m2 so it can be compared between people.
Frequently asked questions
What is body surface area?
Body surface area is an estimate of the total external area of the body, expressed in square meters. Because it tracks body size better than weight alone for many physiological processes, it is widely used in medicine, for example to help calculate certain drug doses.
What is the Mosteller formula for BSA?
The Mosteller formula is BSA in square meters equals the square root of height in centimeters multiplied by weight in kilograms, divided by 3600. It is popular because it is easy to compute yet stays close to older, more complex equations.
How do I calculate BSA for 170 cm and 70 kg?
Multiply 170 by 70 to get 11,900, divide by 3600 to get about 3.306, then take the square root, which is about 1.82. So a person who is 170 cm and 70 kg has a body surface area of roughly 1.82 square meters.
What is a normal body surface area?
There is no single normal value, but most adults fall somewhere between about 1.5 and 2.0 square meters. Adult men average around 1.9 m2 and adult women around 1.6 m2. The figure rises with both height and weight, so taller and heavier people naturally have a larger BSA.
Which BSA formula is most accurate?
No formula is exact, since all are statistical estimates. Mosteller and Du Bois are the most commonly used for adults and agree closely. Haycock is often preferred for children. For clinical use the choice is set by local protocol rather than by which is best in general.
What is the difference between the Mosteller and Du Bois formulas?
Mosteller is a simple square root equation, while Du Bois from 1916 raises height and weight to fixed powers. They usually agree within a couple of percent for average adults, but Du Bois can read slightly lower at very high or very low weights. Mosteller is easier to calculate by hand, which is why this tool uses it.
Why is body surface area used for chemotherapy dosing?
Many chemotherapy drugs are prescribed in milligrams per square meter because organ size, blood volume and metabolic rate scale more closely with surface area than with weight. The oncologist multiplies the prescribed mg/m2 figure by the patient BSA to get the actual dose, following strict protocols this general tool does not replace.
How is BSA used to calculate cardiac index?
Cardiac index equals cardiac output divided by BSA, giving a value in liters per minute per square meter. A normal range is roughly 2.5 to 4.0, and dividing by BSA lets doctors compare heart performance fairly between a small person and a large one.
What is the average BSA for a man and a woman?
Adult men average roughly 1.9 square meters and adult women roughly 1.6 square meters, though both vary widely with height and build. These averages are useful for context but are not targets, since a healthy BSA simply reflects a person body size.
Can I use this BSA result for medication doses?
No. This tool is for general understanding only. Drug dosing follows strict clinical rules about the formula, rounding and any dose caps. Always rely on a qualified clinician and the values in your medical records rather than a general calculator.
Sources
- Simplified Calculation of Body-Surface Area (Mosteller, R.D.) , New England Journal of Medicine (1987)
- Body surface area , National Cancer Institute Dictionary of Cancer Terms
- Body Surface Area (StatPearls) , NCBI Bookshelf